A common problem in the construction business is that of weatherproofing structural junctures, such as that between a vertical wall and a sloped roof. Weatherproofing serves the goal of protecting the underlying structure from the damage associated with water seepage, e.g. rotting of wood, loss of insulation effectiveness and cracking of masonry, and the like. The standard practice is to cover the seams associated with such junctures with flashing.
Typically, such flashing is made of a metal material and is comprised of two planar sections. The planar sections are disposed at some angle relative to each other, resulting in an L-shaped flashing. One section is positioned under the siding and affixed to the vertical wall, and the other section is positioned under the shingles and affixed to the sloped roof. This type of flashing is normally placed along the entire seam created by the juncture.
At the point where the vertical wall and the edge of the sloped roof coincide, however, the flashing is disposed abutting the siding on the vertical wall. Additional sealing is required at this point to prevent water from running off of the flashing, seeping behind the siding and causing damage to the underlying structure. This sealing is usually roof cement or caulking and is applied to the flashing and the siding. The problem with such a method is that due to shrinkage of the caulk over time, thermal expansion and contraction of the dissimilar materials, and weathering, the seal fails and water seeps behind the siding.